package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.util.PriorityQueue;

import java.text.Collator;
import java.util.Locale;

/**
 * Expert: Collects sorted results from Searchable's and collates them. The
 * elements put into this queue must be of type FieldDoc.
 * 
 * <p>
 * Created: Feb 11, 2004 2:04:21 PM
 * 
 * @author Tim Jones (Nacimiento Software)
 * @since lucene 1.4
 * @version $Id: FieldDocSortedHitQueue.java 590530 2007-10-31 01:28:25Z
 *          gsingers $
 */
class FieldDocSortedHitQueue extends PriorityQueue {

	// this cannot contain AUTO fields - any AUTO fields should
	// have been resolved by the time this class is used.
	volatile SortField[] fields;

	// used in the case where the fields are sorted by locale
	// based strings
	volatile Collator[] collators;

	/**
	 * Creates a hit queue sorted by the given list of fields.
	 * 
	 * @param fields
	 *            Fieldable names, in priority order (highest priority first).
	 * @param size
	 *            The number of hits to retain. Must be greater than zero.
	 */
	FieldDocSortedHitQueue(SortField[] fields, int size) {
		this.fields = fields;
		this.collators = hasCollators(fields);
		initialize(size);
	}

	/**
	 * Allows redefinition of sort fields if they are <code>null</code>. This
	 * is to handle the case using ParallelMultiSearcher where the original list
	 * contains AUTO and we don't know the actual sort type until the values
	 * come back. The fields can only be set once. This method is thread safe.
	 * 
	 * @param fields
	 */
	synchronized void setFields(SortField[] fields) {
		if (this.fields == null) {
			this.fields = fields;
			this.collators = hasCollators(fields);
		}
	}

	/** Returns the fields being used to sort. */
	SortField[] getFields() {
		return fields;
	}

	/**
	 * Returns an array of collators, possibly <code>null</code>. The
	 * collators correspond to any SortFields which were given a specific
	 * locale.
	 * 
	 * @param fields
	 *            Array of sort fields.
	 * @return Array, possibly <code>null</code>.
	 */
	private Collator[] hasCollators(final SortField[] fields) {
		if (fields == null)
			return null;
		Collator[] ret = new Collator[fields.length];
		for (int i = 0; i < fields.length; ++i) {
			Locale locale = fields[i].getLocale();
			if (locale != null)
				ret[i] = Collator.getInstance(locale);
		}
		return ret;
	}

	/**
	 * Returns whether <code>a</code> is less relevant than <code>b</code>.
	 * 
	 * @param a
	 *            ScoreDoc
	 * @param b
	 *            ScoreDoc
	 * @return <code>true</code> if document <code>a</code> should be sorted
	 *         after document <code>b</code>.
	 */
	protected final boolean lessThan(final Object a, final Object b) {
		final FieldDoc docA = (FieldDoc) a;
		final FieldDoc docB = (FieldDoc) b;
		final int n = fields.length;
		int c = 0;
		for (int i = 0; i < n && c == 0; ++i) {
			final int type = fields[i].getType();
			switch (type) {
			case SortField.SCORE: {
				float r1 = ((Float) docA.fields[i]).floatValue();
				float r2 = ((Float) docB.fields[i]).floatValue();
				if (r1 > r2)
					c = -1;
				if (r1 < r2)
					c = 1;
				break;
			}
			case SortField.DOC:
			case SortField.INT: {
				int i1 = ((Integer) docA.fields[i]).intValue();
				int i2 = ((Integer) docB.fields[i]).intValue();
				if (i1 < i2)
					c = -1;
				if (i1 > i2)
					c = 1;
				break;
			}
			case SortField.LONG: {
				long l1 = ((Long) docA.fields[i]).longValue();
				long l2 = ((Long) docB.fields[i]).longValue();
				if (l1 < l2)
					c = -1;
				if (l1 > l2)
					c = 1;
				break;
			}
			case SortField.STRING: {
				String s1 = (String) docA.fields[i];
				String s2 = (String) docB.fields[i];
				// null values need to be sorted first, because of how
				// FieldCache.getStringIndex()
				// works - in that routine, any documents without a value in the
				// given field are
				// put first. If both are null, the next SortField is used
				if (s1 == null)
					c = (s2 == null) ? 0 : -1;
				else if (s2 == null)
					c = 1; // 
				else if (fields[i].getLocale() == null) {
					c = s1.compareTo(s2);
				} else {
					c = collators[i].compare(s1, s2);
				}
				break;
			}
			case SortField.FLOAT: {
				float f1 = ((Float) docA.fields[i]).floatValue();
				float f2 = ((Float) docB.fields[i]).floatValue();
				if (f1 < f2)
					c = -1;
				if (f1 > f2)
					c = 1;
				break;
			}
			case SortField.DOUBLE: {
				double d1 = ((Double) docA.fields[i]).doubleValue();
				double d2 = ((Double) docB.fields[i]).doubleValue();
				if (d1 < d2)
					c = -1;
				if (d1 > d2)
					c = 1;
				break;
			}
			case SortField.CUSTOM: {
				c = docA.fields[i].compareTo(docB.fields[i]);
				break;
			}
			case SortField.AUTO: {
				// we cannot handle this - even if we determine the type of
				// object (Float or
				// Integer), we don't necessarily know how to compare them (both
				// SCORE and
				// FLOAT contain floats, but are sorted opposite of each other).
				// Before
				// we get here, each AUTO should have been replaced with its
				// actual value.
				throw new RuntimeException(
						"FieldDocSortedHitQueue cannot use an AUTO SortField");
			}
			default: {
				throw new RuntimeException("invalid SortField type: " + type);
			}
			}
			if (fields[i].getReverse()) {
				c = -c;
			}
		}

		// avoid random sort order that could lead to duplicates (bug #31241):
		if (c == 0)
			return docA.doc > docB.doc;

		return c > 0;
	}
}
